pablode / guc Goto Github PK

guc has a version defined in the top-level CMakeLists.txt, but it is not propagated to the library and application. We should

• introduce a --version flag to the executable
• #define the major, minor and patch version numbers in the libguc header
• write the exact guc version string to the asset Documentation metadatum

Furthermore, it might make sense to include the commit hash in non-release version strings.

Hi! I tried to get guc working with the custom resolver I've been working on but unfortunately it fails upon trying to load the file:
Failed to open "iroh://doc/pajzuzssv2l7wg7iruxixkbc7nfcm42gqfqbmzz5hux4im4v2yea/m5wfirrpirqw2ylhmvseqzlmnvsxilthnr2gmaa.gltf" - unable to parse glTF file: file not found

The problem is that this code assumes that resolvedPath is on the local filesystem:

Ideally you'd call something like ArGetResolver().OpenAsset(resolvedPath) to get an ArAsset and then use the bytes from ArAsset::GetBuffer to load the glTF data. This is a bit of a hastle not gonna lie, but it would mean that assets using custom URI schemas (iroh:// for me, but also http://) would load perfectly.

We can create a displayColor primvar with 'constant' interpolation by taking the base_color factor or average texture color. It might even be possible to extract vertex colors by unwrapping the UV coordinates.

The generated values are not vertex colors and they should not be referenced by the MaterialX shading graph.

Extension spec: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_unlit

The extension can not be correctly represented with a UsdPreviewSurface, but we might be able to emulate it using the emissive color.

In MaterialX, this feature should be covered by the recently introduced 'unlit' shader node: AcademySoftwareFoundation/MaterialX#860

Currently, many errors which occur during conversion are fatal. Revisit some of the handling since an asset with a missing material or mesh is more useful than no asset at all.

Similar to usd_from_gltf, we could provide an Sdf file format plugin which implicitely converts glTF to USD+MaterialX files.

glTF animations are currently not supported. They are described in spec section 3.11.

Set up the testing infrastructure for..

• Unit tests
• File tests with..
  • Khronos's sample models
  • Khronos's validation models
  • Custom models
• Reference images

Some open questions are:

• do we put file tests in a separate repo?
• what reference renderer to use?
  • USD+MaterialX is barely supported; gatling could be used in the future

NVIDIA distributes an MDL implementation of the glTF PBR as part of the MDL SDK: https://github.com/NVIDIA/MDL-SDK/blob/master/examples/mdl/nvidia/sdk_examples/gltf_support.mdl

It supports all material extensions except unlit and seems straightforward to implement.

The USD glossary says:

Gprims are boundable, and should always submit to computing an extent (even if it be an empty extent), and valid UsdGeom scene description should always provide an authored extent on a gprim that captures its changing shape (if its shape is animated).

We therefore should calculate a prim's bounding box and call SetExtentsHint.

Extension spec: https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_materials_variants/README.md

USD has native support for variants. Mapping should be quite easy.

Set up GitHub Actions pipelines to produce binaries for Windows, Linux and MacOS. Consider using a USD docker image from the aswf-docker repo.

Currently, libguc prints error messages and returns false on convert(..). But calling applications may want to handle different types of errors differently. Identify error groups and return error codes instead.

Small but important fix in makeStSetName(). The index should only be appended if the index is > 0.

Unfortunately, there are multiple issues with UsdUtilsCreateNewUsdzPackage when it comes to layer referencing:

1. the function can't seem to properly export the referenced .mtlx file
2. even when inlining MaterialX as UsdShade, the referenced images are omitted

These two bug reports might be related:

• PixarAnimationStudios/OpenUSD#1543 (comment)
• https://groups.google.com/g/usd-interest/c/jos8g0t8w00/m/-9OG2nQZBQAJ

Extension spec: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_transform

It should be mappable to the UsdShade Transform2d node and MaterialX's place2d node.

glTF supports an arbitrary number of COLOR accessors. We should expose them in a way while still translating COLOR_0 to displayColor, preferably without duplicate data.

See also: https://groups.google.com/g/usd-interest/c/VOkh0aj-8bU/m/zxrMQ-pJAgAJ

Translate the 'extras' field of all glTF entities into a corresponding USD representation. Do we want to dump a single metadatum or do we additionally decode key-value dicts?

Do you happen to have more detailed instructions on how to build this for someone who has never used cmake? Unsure how to build it after cloning the repository.

Skinning (glTF spec 3.7.3) is currently not supported. We should be able to map it to the UsdSkel API.

guc automatically generates unique names for prims, shading nodes and image files. This functionality is not covered by the Khronos validation and sample models. Custom test assets need to be created.

Currently, meshes, cameras, lights and materials are instanced. But the glTF scenegraph is a DAG, which means that hierarchy parts can be instanced, too. Can this behaviour be replicated with USD?

Use 'group', 'assembly', 'component' and 'subcomponent' kind metadata of the UsdModelAPI to classify prims.

The glossary has an overview: https://graphics.pixar.com/usd/release/glossary.html#usdglossary-kind